In general, the invention features improved methods for cloning mammals and methods for inserting chromosomes, nuclei, or chromatin masses into recipient cells.
The cloning of mammals allows the production of multiple mammals with an identical DNA content. The donor genetic material used to generate these mammals may be selected or engineered such that the cloned mammals have desirable properties, such as increased resistance to disease. Unfortunately, the efficiency of cloning mammals using donor somatic cells is generally low, resulting in only about 1–2% of nuclear transplant embryos developing to term (Polejaeva et al, Nature 407:86–90, 2000). A significant problem with cloning is the loss of mid to late term pregnancies and the low viability of the offspring. Thus, more efficient methods are needed for cloning mammals. These improved methods may reduce the cost and time required to generate multiple viable offspring.